1. Field of the Invention
An acoustic inspection device, namely one that has a small footprint, exposes the workpiece to few contaminants, rapidly establishing coupling with the workpiece, requires less couplant than earlier devices, and a small localized couplant chamber to wet the workpiece without placement in an immersion bath.
2. Description of the Prior Art
Nondestructive Inspection (NDI) determines the quality of a workpiece without causing damage to the workpiece. One prior art NDI technique uses acoustic waves to inspect a workpiece: this technique directs an incident acoustic wave at a workpiece and analyzes the reflection to determine the workpiece's quality. Acoustic inspection is helpful, for example, to determine the integrity of airplane components including the wing, fuselage and empennage by detecting disbanded lap-splices, corroded rivet joints, and similar structural defects. Acoustic inspection is also helpful, for example, to determine the integrity of automobile, electronic, and microelectromechanical systems (MEMS) components, including resistance spot and line welds by detecting unsatisfactory spot welds, disbonded lap splices, butt welded joints, and similar joining techniques using a wide variety of materials and surface finishes including high strength steels, aluminum, plastics, ceramics, and composites.
A typical apparatus for acoustically inspecting a workpiece includes a pulse generator electrically connected to a transducer assembly that generates a focused acoustic wave. The acoustic wave travels through a transmission medium and onto the workpiece. Acoustic reflections from the workpiece radiate back to the transducer and cause the transducer to generate a corresponding electrical signal. An operator or a computer processor then analyzes the electrical signal to determine the quality of the workpiece.
Ultrasonic NDI, in particular, can improve the inspection spatial resolution and the signal to noise by using a focused acoustic beam that may be focused by electronic or ultrasonic lenses. It is noteworthy that even so-called flat-focused transducers exhibit a natural focus that may or may not be used as a focused transducer. Also, mechanical or electronic scanning methods may be used to cause the ultrasonic beam to scan over the workpiece. In all of these cases, Ultrasonic NDI requires quality and reliable acoustic coupling without introducing spurious signals; and, the effectiveness of any given technique can be compared for reference purposes to the performance of a similar transducer used in a water immersion mode.
Known related inspection apparatus are described by Fleming in the U.S. Pat. No. 6,298,727 and Patton in the U.S. Pat. No. 5,469,744 uses an acoustic apparatus called a Contact Adaptive Bubbler (CAB). These CABs consist of a tubular member containing an ultrasonic transducer, a couplant chamber, and a couplant reservoir between the transducer and the workpiece. A membrane that generally avoids contact with the workpiece is used to separate the couplant chamber and the couplant reservoir. Couplant is continuously supplied to replenish couplant leaks. A vacuum chamber recovers couplant that leaks from the couplant reservoir.
However, in practice, it has been found that CAB devices are too large in overall size and footprint and too costly for many applications. Attempts to reduce CAB size have introduced ultrasonic signal attenuation, unwanted or spurious signals and unreliable ultrasonic coupling. Additionally, in some applications, large size hoses are required for both the couplant supply and the vacuum couplant recovery lines to the CABs; these large lines create undesirable forces that easily disturb the orientation of the CAB device relative to the workpiece. Additionally, larger CAB footprints limit their use near surface obstructions and near workpiece edges where ultrasonic coupling is lost. Finally, the larger CAB devices require larger couplant supplies and ancillary equipment, thereby restricting applications and portability.
What is needed is a smaller CAB device that provides reliable ultrasonic coupling. Such a CAB device needs to have a small size and a small footprint, require small amounts of couplant and vacuum, and adapts to manual and automated scanning techniques. The present invention provides such a smaller CAB device.